1. Field of the Invention
The present invention relates to a method for manufacturing sintered parts by the powder metallurgy method.
2. Description of the Prior Art
Conventionally, it has been difficult to mold sintering materials obtained by the powder compression molding technique into articles having complicated shapes (i.e. complicated articles).
Recently, powder injection molding techniques capable of molding complicated articles which cannot be obtained by the conventional compression molding has aggressively been developed (for example, disclosed in the Japanese Patent Application No. SHO 62-33282). Such a powder injection molding method includes the steps of adding an organic binder to an inorganic material to provide flowability thereto and removing the organic binder from the material by a debinder process prior to sintering.
However, the method, having a great difficulty in removing the organic binder, takes much time to prevent any defects from occurring to the products, or causes the products to be limited to small-sized ones. This problem becomes more significant especially as the powder becomes finer.
Therefore, as another example, it has been proposed that part of the binder is eluted in a solvent (disclosed in U.S. Pat. No. 4,765,950). The elution method using a solvent facilitates the removal of the organic binder.
In the method according to the U.S. Pat. No. 4,765,950, however, the solvent to be used is in the chlorine or ketone series, which is hard to industrially use because of the influence on the human body. Also, the binder soluble in the solvent is of liquid phase at room temperature, which causes a problem that an injection molded product is extremely low in strength.